1. Field of the Invention
The present invention generally relates to a swash plate type compressor, and, more particularly, to an improvement in the bearings that receive a load on the swash plate.
2. Description of the Related Art
In general, compressor units used in automobiles, trucks and the like are used to supply compressed gas to the vehicle's air conditioning system. One common type of compressor utilizes a swash plate design having a plurality of double-headed pistons. The swash plate type compressor has a pair of cylinder blocks 110A and 110B as shown in FIG. 13. A drive shaft 111 is rotatably supported by the pair of cylinder blocks 110A and 110B. A swash plate 112 is mounted on the drive shaft 111. Thrust bearings 113 are respectively located between annular pressure receiving rib portions 112a, provided on the front and rear surfaces of the swash plate 112, and pressure receiving rib portions 110a of the cylinder blocks 110A and 110B. Each-thrust bearing 113 has an annular inner race 113a and an annular outer race 113b which have different diameters.
The outer ends of both cylinder blocks 110A and 110B respectively abut housings 114 and 115. Bolts 116 securely fix the individual cylinder blocks 110A and 110B and the housings 114 and 115.
During the compressor's assembly, when the bolts 116 are tightened, each inner race 113a abuts on the associated pressure receiving rib portion 112a near its outer periphery. This bolt tightening action elastically deforms each inner race. The outer races 113b abut on the pressure receiving rib portions 110a of the cylinder blocks 110A and 110B in the vicinity of their inner peripheries.
When the swash plate 112 rotates, the pistons 117 reciprocate, compressing the refrigerant gas. The reaction force of the swash plate 112, in turn, acts as an axial load on the thrust bearings 113 via the pistons 117 and the swash plate 112. The axial load is applied to the thrust bearings 113 by pressure receiving rib portions 110a, 112a. Since the diameter of rib portion 112a is larger than that of rib portion 110a, a moment is created around the inner race 112a causing it to elastically deform when the axial load is applied to the bearings 113 by the swash plate 112. As schematically illustrated in FIG. 14, the thrust bearings 113 can be considered as equivalent to springs S positioned between both sides of the swash plate 112 and the cylinder blocks 110A and 110B.
At the time the refrigerant gas is compressed, however, the spring like action of the thrust bearings 113 sets up a vibration which is transmitted to the swash plate 112. Moreover, under conditions when the drive shaft rotates at high speeds, a high frequency vibration is created and contributes to the noise produced by the compressor.
Japanese Unexamined Utility Model Publication No. 54-170410 discloses the structure of another thrust bearing. According to this structure, both outer surfaces of the boss portions of the swash plate and the two support surfaces of the cylinder blocks are formed flat. Here, the thrust bearings are held rigid between the outer surfaces of the boss portions and the opposing support surfaces. This structure makes it difficult to adjust the amount of force needed to fasten the bolts 116 to the housings 114 and 115. For example, if aluminum alloy components are fastened by the bolts, the thermal expansion of the aluminum components increases the difficulty of adjusting the amount of force needed to fasten the bolts 116 to the housings 114 and 115.
Further, when some moment is applied to the swash plate due to the pressure of the compressed gas, an offset load is applied to the rollers in the thrust bearing. This hastens the wearing of the bearing. The worn thrust bearings, in turn, cause vibration and noise or power loss in the compressor.